Metal filters have long been used for a variety of applications. For example, porous stainless steel filters prepared from sintered metal particulate, e.g., stainless steel powder, have found use in a variety of processes where high pressure drops are acceptable and in applications where relatively fine filtration capability must be combined with mechanical strength, resistance to high temperatures and/or resistance to chemical attack. Such applications include the filtration of fine catalysts used in fluidized bed catalytic processes where elevated temperatures are encountered, e.g., fluid cat cracking, and in the manufacture of high fidelity recording tapes.
Still another use of such filters is in the filtration of molten resin used in the manufacture of polymeric films and fibers as, for example, polyester film.
Metal filters formed from wire mesh screen have also found use in applications where mechanical strength must be combined with resistance to high temperatures and/or resistance to chemical attack. This type of filter has the desirable characteristic of being readily corrugated to provide a high surface area filter for use in a limited space. It suffers, however, from low efficiency for removal of fine particles due to the relatively large pore sizes of the wire mesh structure.
The range of applications for metal filters could be greatly expanded if a filter structure combining the relatively fine pore structure of the conventional sintered metal particulate filter could be combined with the ability to corrugate or pleat the filter structure to increase the filter surface area available in a limited space while maintaining a fine pore structure. Further, if the pore sizes of conventional sintered metal filters could be further reduced, while concomitantly rendering such structures capable of being finely corrugated, the range of applications would be even further broadened.
Commercially available porous metal material prepared from metal powders is generally relatively thick. And, while such material can be bent into cylindrical shape, the inside radii (bending radii) of the resulting cylinder is generally no less than about seven times the thickness of the metal. As a result, corrugated (pleated) structures prepared from such material have limited practical application.